The SIR provided Telluromethionine; 1 g A simple and efficient method for the specific replacement of the naturally occurring amino acid methionine by telluromethionine in the expression of recombinant proteins has been described (J. Mol. Biol. 1997, 270, 616-623). We would like to apply this system for the production of telluromethionine-proteins as heavy atom derivitives to help aid in the structure determination of a penicillin-resistant PBP and an enzyme from the folate pathway in Bacteria. The resulting structural information will be the basis for the rational design of new inhibitors of these enzymes.